1. Field of the Invention
The present invention relates to a printing apparatus that prints an image on a sheet in an ink jet system.
2. Description of the Related Art
Japanese Patent Laid-Open No. 2005-74746 discloses an ink jet printing apparatus capable of ejecting ink from a print head to perform printing on both surfaces of a sheet. This apparatus is configured in such a manner as to enable printing on both surfaces, that is, the obverse and reverse of a sheet by a single printing unit. The sheet having an image printed on the obverse thereof in the printing unit is turned upside down on a reversing path, and then, is subjected to printing on its reverse in the printing unit again. Moreover, there is provided a sensor for detecting the passage of the sheet on a sheet conveyance path. Therefore, an arm of the sensor is brought into contact with the sheet when a sheet tip passes the sensor so that the sensor is turned ON, and thus, the sensor can recognize the passage of the sheet.
In order to increase the total throughput of double-sided printing, a sheet needs to be conveyed at a higher speed. However, as disclosed in Japanese Patent Laid-Open No. 2005-74746, an apparatus for performing double-sided printing by the single printing unit on the reversing path is configured to have a complicated reversing path. As a consequence, a jam (i.e., a paper jam) is liable to occur during sheet conveyance in such an apparatus, and therefore, it is difficult to increase a sheet conveyance speed. An increase in sheet conveyance speed also signifies that there is not much time required for drying ink. If the arm of the sensor is brought into contact with a printed image while the sheet is moved when the ink applied onto the sheet is not dried yet, a smudged trace remains on a final image. That is to say, the fear of a problem of a so-called smear is increased.